Glass stress measurement using fluorescence

Abstract

An apparatus and method for measurement of the stress in and thickness of flat glass or curved glass segments is disclosed that uses fluorescence to quickly and accurately ascertain both the thickness of the stress layers and the wall thickness in addition to the stress curve in flat glass or curved glass segments. The apparatus and method may be used to quickly and accurately measure both the stress in and the thickness of flat glass or curved glass segments at a plurality of various locations therein. The apparatus and method are adapted for large scale flat glass or curved glass segment manufacturing, and are capable of high speed measurement of the stress in and the thickness of the flat glass or curved glass segments.

1. An apparatus for measuring stress in a segment of glass, comprising:
 a light beam source that generates a light beam; 
 light beam coupling apparatus for directing said light beam at the side of a segment of glass at an angle facilitating entry of said light beam into and through the side of the segment of glass, said light beam causing fluorescent light to be emitted within the segment of glass in response to said light beam within the side of the segment of glass; 
 fluorescent light coupling apparatus for coupling a portion of said fluorescent light emitted in response to said light beam within the segment of glass outwardly from the side of the segment of glass; and 
 fluorescent light processing and analysis apparatus that processes the fluorescent light exiting the side of the segment of glass and determines the stress in the segment of glass from the processed fluorescent light exiting the side of the segment of glass. 
 
     
     
       2. As apparatus as defined in  claim 1 , wherein said light beam source comprises:
 a laser that produces a light beam which is linearly polarized. 
 
     
     
       3. As apparatus as defined in  claim 2 , wherein said light beam source additionally comprises:
 polarization adjustment apparatus which is adjustable to rotate the polarization of said linearly polarized light beam to a desired orientation that will produce an the largest possible fluorescent light emitted in response to said light beam within the segment of glass. 
 
     
     
       4. As apparatus as defined in  claim 3 , wherein said polarization adjustment apparatus comprises:
 laser mounting apparatus for securing said laser in position, wherein said laser mounting apparatus selectively allows said laser to be rotated to thereby rotate the polarization of said linearly polarized light beam to a desired orientation. 
 
     
     
       5. As apparatus as defined in  claim 3 , wherein said polarization adjustment apparatus comprises:
 a half wave plate located intermediate said laser and said light beam coupling apparatus, said half wave plate being selectively rotatable to thereby rotate the polarization of said linearly polarized light beam to a desired orientation. 
 
     
     
       6. As apparatus as defined in  claim 1 , wherein said light beam coupling apparatus and said fluorescent light coupling apparatus collectively comprise:
 an optical coupling member for location adjacent the side of the segment of glass, said light beam being directed onto said optical coupling member whereupon said optical coupling member directs said light beam into the side of the segment of glass, said fluorescent light emitted from the side of the segment of glass being collected by said optical coupling member whereupon said optical coupling member directs the emitted fluorescent light into fluorescent light processing and analysis apparatus. 
 
     
     
       7. As apparatus as defined in  claim 6 , wherein said optical coupling member comprises:
 a coupling prism. 
 
     
     
       8. As apparatus as defined in  claim 6 , wherein said optical coupling member is arranged and configured to couple said light beam into the segment of glass and to couple said emitted fluorescent light out of said segment of glass using air as a coupling medium. 
     
     
       9. As apparatus as defined in  claim 8 , wherein said optical coupling member is arranged and configured to couple said light beam into the segment of glass at a compound angle that comprises an angle of between approximately 40 degrees and approximately 70 degrees from a plane normal to the surface of the glass container at the point of entry, and at an approximately 45 degree angle out of said plane. 
     
     
       10. As apparatus as defined in  claim 9 , wherein said optical coupling member is arranged and configured to couple said light beam into the segment of glass at a compound angle that comprises an angle of between approximately 60 degrees from said plane normal to the surface of the glass container at the point of entry, and at an approximately 45 degree angle out of said plane. 
     
     
       11. As apparatus as defined in  claim 6 , additionally comprising:
 apparatus for directing a stream of liquid coupling fluid intermediate said optical coupling member and the segment of glass to optically couple said light beam into the segment of glass and to couple said emitted fluorescent light out of the segment of glass; 
 
       wherein said optical coupling member is arranged and configured to facilitate the coupling of said light beam into the segment of glass and to facilitate the coupling of said emitted fluorescent light out of the segment of glass. 
     
     
       12. As apparatus as defined in  claim 11 , wherein said optical coupling member is arranged and configured to couple said light beam into the segment of glass at a compound angle that comprises an angle of between approximately 40 degrees and approximately 70 degrees from a plane normal to the surface of the segment of glass at the point of entry, and at an approximately 45 degree angle out of said plane. 
     
     
       13. As apparatus as defined in  claim 12 , wherein said optical coupling member is arranged and configured to couple said light beam into the segment of glass at a compound angle that comprises an angle of between approximately 45 degrees from the normal to the surface of the segment of glass at the point of entry in said plane orthogonal to an axis of the glass container, and at an approximately 45 degree angle from said plane. 
     
     
       14. As apparatus as defined in  claim 1 , wherein said fluorescent light processing and analysis apparatus comprises:
 fluorescent light processing apparatus that processes said fluorescent light exiting the side of the segment of glass to produce processed fluorescent light; and 
 fluorescent light analysis apparatus that analyzes the processed fluorescent light to derive information indicative of the stress in the segment of glass. 
 
     
     
       15. As apparatus as defined in  claim 14 , wherein said fluorescent light processing apparatus comprises:
 a quarter wave plate located intermediate said fluorescent light coupling apparatus and said fluorescent light analysis apparatus to linearly polarize said fluorescent light exiting the side of the segment of glass, wherein said quarter wave plate has an axis that is aligned at an angle of approximately 45 degrees with respect to a linearly polarized portion of said fluorescent light exiting the side of the segment of glass. 
 
     
     
       16. As apparatus as defined in  claim 15 , wherein said fluorescent light processing apparatus additionally comprises:
 an apparatus located intermediate said quarter wave plate and said fluorescent light analysis apparatus for generating two images of ideally orthogonal polarization states of the linearly polarized portion of said fluorescent light exiting the side wall of the segment of glass. 
 
     
     
       17. As apparatus as defined in  claim 16 , wherein said apparatus for generating two images comprises:
 a polarization rotator for alternately modulating the polarization state of the linearly polarized portion of said fluorescent light exiting the side of the segment of glass plus and minus 45 degrees with respect to said axis of said quarter wave plate. 
 
     
     
       18. As apparatus as defined in  claim 17 , wherein said polarization rotator comprises:
 a rotator drive producing alternating positive and negative voltages; and 
 a ferroelectric liquid crystal element that is driven by said alternating positive and negative voltages from said rotator drive. 
 
     
     
       19. As apparatus as defined in  claim 17 , wherein said fluorescent light analysis apparatus comprises:
 a camera for acquiring a first image through said polarization rotator of the modulated linearly polarized portion of said fluorescent light exiting the side of the segment of glass at plus 45 degrees with respect to said axis of said quarter wave plate and a second image through said polarization rotator of the modulated linearly polarized portion of said fluorescent light exiting the side of the segment of glass at minus 45 degrees with respect to said axis of said quarter wave plate; and 
 an image differentiator for differentiating said first and second images to produce a normalized difference image characteristic of the stresses throughout the thickness of the segment of glass. 
 
     
     
       20. As apparatus as defined in  claim 19 , wherein said fluorescent light analysis apparatus additionally comprises:
 an image processor for processing said normalized difference image to produce at least one of a retardance curve and a stress parabola for the segment of glass. 
 
     
     
       21. As apparatus as defined in  claim 16 , wherein said apparatus for generating two images comprises:
 a polarizing beam splitter prism having as an input the linearly polarized portion of said fluorescent light exiting the segment of glass, wherein said polarizing beam splitter prism has as outputs said two images of ideally orthogonal polarization states of the linearly polarized portion of said fluorescent light exiting the segment of glass. 
 
     
     
       22. As apparatus as defined in  claim 21 , wherein said fluorescent light analysis apparatus comprises:
 a pair of cameras for respectively acquiring said two images of ideally orthogonal polarization states of the linearly polarized portion of said fluorescent light exiting the segment of glass; and 
 an image differentiator for differentiating said two images from said pair of cameras to produce a normalized difference image characteristic of the stresses throughout the thickness of the segment of glass. 
 
     
     
       23. As apparatus as defined in  claim 22 , wherein said fluorescent light analysis apparatus additionally comprises:
 an image processor for processing said normalized difference image to produce at least one of a retardance curve and a stress parabola for the segment of glass. 
 
     
     
       24. As apparatus as defined in  claim 14 , wherein said fluorescent light processing apparatus additionally comprises:
 a filter that passes fluorescent light but not light at the frequency of said light beam source, said filter being located intermediate the side wall of the segment of glass and said fluorescent light analysis apparatus. 
 
     
     
       25. As apparatus as defined in  claim 24 , wherein said filter comprises:
 one of the group consisting of a long pass filter that passes fluorescent light, a band pass filter that passes fluorescent light, and a notch filter that passes fluorescent light. 
 
     
     
       26. As apparatus as defined in  claim 1 , additionally comprising:
 scanning apparatus for moving said apparatus for measuring stress in a segment of glass to a plurality of positions adjacent different locations on the side of the segment of glass. 
 
     
     
       27. An apparatus for measuring stress in a segment of glass, comprising:
 a light beam source that generates a linearly polarized light beam; 
 light beam coupling apparatus for directing said linearly polarized light beam at the side of a segment of glass at an angle facilitating entry of said light beam into and through the side of the segment of glass, said linearly polarized light beam causing fluorescent light to be emitted within the segment of glass in response to said linearly polarized light beam within the segment of glass; 
 fluorescent light coupling apparatus for coupling a portion of said fluorescent light emitted in response to said linearly polarized light beam within the segment of glass outwardly from the side of the segment of glass; 
 a camera for acquiring images of the processed fluorescent light exiting the side of the segment of glass; and 
 fluorescent light analysis apparatus that analyzes the processed fluorescent light to derive information indicative of the stress in the side of the segment of glass. 
 
     
     
       28. An apparatus for measuring stress in a segment of glass, comprising:
 a light beam source that generates a light beam; 
 light beam coupling apparatus for directing said light beam at the side of a segment of glass at an angle facilitating entry of said light beam into and through the side of the segment of glass, said light beam causing fluorescent light to be emitted within the segment of glass in response to said light beam within the segment of glass; 
 fluorescent light coupling apparatus for coupling a portion of said fluorescent light emitted in response to said light beam within the segment of glass outwardly from the side of the segment of glass; and 
 fluorescent light processing apparatus that processes the fluorescent light exiting the side of the glass container to determine a stress profile in the side of the segment of glass. 
 
     
     
       29. A method for measuring stress in a segment of glass, comprising:
 directing a light beam at the side of a glass container at an angle facilitating entry of the light beam into and through the side of the segment of glass; 
 detecting fluorescent light emitted in response to the light beam within the segment of glass which fluorescent light exits the side of the segment of glass; and 
 processing the fluorescent light exiting the side of the segment of glass and analyzing the processed fluorescent light exiting the side of the segment of glass to determine the stress in the segment of glass.